1. Field
The present invention relates to a substrate handler, a lithographic apparatus and a method for manufacturing a device.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which may be referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern may be transferred on (part of) the substrate (e.g., a glass plate), e.g., via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning device may be used to generate other patterns, for example a color filter pattern, or a matrix of dots. Instead of a mask, the patterning device may comprise a patterning array that comprises an array of individually controllable elements. A benefit of such a system compared to a mask-based system is that the pattern may be changed more quickly and for less cost.
A flat panel display substrate may be rectangular in shape. Lithographic apparatus designed to expose a substrate of this type may provide an exposure region which covers a full width of the rectangular substrate, or which covers a portion of the width (for example half of the width). The substrate may be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through the projection beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate, then exposure may be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate may be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
The known lithographic apparatus comprises a substrate handler for loading and/or unloading a substrate on/from the substrate table, respectively. This known substrate handler comprises a conditioning device for conditioning a substrate before the substrate is loaded on the substrate table. Such conditioning process comprises bringing the substrate to a relative uniform temperature. For instance, the temperature of a substrate before conditioning may be 23±2° C. while after conditioning the temperature within the substrate may be brought to a range of 23±0.03° C. The conditioning device of the known substrate handler comprises a conditioning water circuit which is integrated in under the support surface of substrate handler. During conditioning the substrate rests on the support surface, whereby the constant temperature of the support surface which results from the conditioning water circuit, provides for the conditioning of the substrate.
However, due to irregularities, such as cutouts or discontinuities, in the support surface which have to be present for handling the substrate, it may be difficult to obtain a uniform temperature in the substrate supported on the support surface. Such irregularities for instance comprise grooves for accommodating gripping fingers of a gripping device, openings for accommodating a lifting device, such as E-pins, for lifting a substrate from the support surface to make exchange with a robot possible, and pimples provided on the table to avoid the transfer of particles from substrate handler to the substrate table on which the pattern is projected on the substrate.
For example, the temperature offset of a part of the substrate above a cutout (for example a groove with a width of 7 mm) may be about 1° C. This may result in a non-uniform thermal expansion of the substrate (perpendicular to the grooves about 22 nm per groove of 7 mm width, which results with 18 grooves per substrate in about 400 nm total expansion per substrate; and in the direction of the grooves an expansion of more than 1 μm). Such non-uniform thermal expansion is generally unacceptable for the application of the substrate in a lithographic apparatus, since it may lead to non-uniform quality of the substrate products.
The influence of irregularities in the support surface becomes for example apparent when glass substrates are conditioned on a support surface of a substrate handler. In order to obtain a substantially uniform temperature distribution in the substrate, it is desirable to considerably increase the conditioning time, compared to a support surface without such irregularities. For instance, when the conditioning time for a substrate on a support them surface without grooves is about 15 seconds, the conditioning time for a substrate on a similar support surface that is provided with grooves may be over 120 seconds. This results in a lower throughput of the substrate handler, and therewith possibly a lower throughput of the lithographic apparatus. Such lower throughput is undesirable.
This effect caused by irregularities in the support surface of the substrate handler may also be present when conditioning other substrates such as for instance Si-substrates. As a consequence, the throughput of such substrates in the substrate handler shall be relatively lower when grooves or other irregularities are present, since the conditioning time needed to obtain a uniform temperature distribution in the substrate is longer.
It is desirable that the bottom side of the substrate be free of any particles such as dust, when the substrate is laid down on the support surface of the substrate table for the conditioning thereof. This contamination is in particular not desirable as these particles may be transferred with the substrate to the substrate table, where they form a risk for final product quality. Moreover, the particles may after being transferred to the substrate table, stick to the support surface of the substrate table and therefor form a considerable risk for the product quality of substrates which are subsequently put on the substrate table for an exposure process.